This invention relates to a halophosphate phosphor having novel composition and a fluorescent lamp using the same. More particularly, it relates to a halophosphate phosphor being capable of emitting a stable blue-green light with high emission efficiency and having a less afterglow after the excitation has been removed, and a fluorescent lamp using the same, especially a high color rendering fluorescent lamp whose emitted color temperature is 4,200 to 5,600 K (Kelvin) and color rendering classification belongs to the so-called EDL type corresponding to AAA type according to Japanese Industrial Standard Z9112-1983.
Halophosphate phosphors activated with divalent europium emit blue-green light as disclosed in U.S. Pat. No. 4,500,443. These phosphors are known to emit a stable light with high efficiency and be useful for, particularly, preparation of a blue-green phosphor for the above-mentioned EDL type high color rendering fluorescent lamp. However, the halophosphate phosphors activated with divalent europium may generate an afterglow (a phenomenon in which luminescence remains after the excitation has been removed) depending on the mixing proportions between alkaline earth metals such as barium, calcium and magnesium contained therein.
When the fluorescent lamps are prepared by use of such phosphors which may readily generate the afterglow, no serious inconveniences will arise when they are used at ordinary places and forms. However, in special places such as a darkroom in a color photograph processing laboratory, the afterglow which remains immediately after the lamp has been put out may give bad influences to photosensitive papers or films.